1. Field of the Invention
The present invention relates to a heat exchanger for use as an evaporator or a condenser for an air conditioner, a radiator or heater core for vehicle, or other type heat exchanger. The invention further relates to methods for manufacturing header pipes of a heat exchanger and for connecting the header pipes and tubes in the heat exchanger.
2. Description of the Prior Art
FIGS. 17 and 18 show a typical conventional heat exchanger which allows heat to exchange between a heat exchange medium (for example, a cooling medium or a brine) flowing in the heat exchanger and air passing through the heat exchanger. A heat exchanger 21, as shown in FIG. 17, is comprised of a pair of header pipes 22 extending in parallel relation to each other, a plurality of tubes 23 disposed between the header pipes and connected to the header pipes at their end portions with a predetermined pitch in the vertical direction, a plurality of radiation fins 24 provided on the sides of the tubes, and a pair of reinforcement members 25 disposed on the top and bottom radiation fins.
Each header pipe 22 is constructed from an welded aluminium pipe. A plurality of connection holes 26 are formed on the periphery of the header pipe 22 with a predetermined pitch in the axial direction of the header pipe. The end portion of each tube 23 is inserted into a corresponding connection hole 26 so that the inside of the tube communicates with the inside of the header pipe 22. Both ends of each header pipe 22 are closed by caps 27. An inlet tube (not shown) for introducing the heat exchange medium into heat exchanger 21 is connected to one of the header pipes 22, and an outlet tube (not shown) for delivering the heat exchange medium out from heat exchanger 21 is connected to the other header pipe.
Each tube 23 is formed as a straight tube which is flattened in the horizontal direction. The end portions of tube 23 are inserted into connection holes 26 of header pipes 22, and fixed therein by, for example, brazing. Corrugate type radiation fins 24 are fixed on the upper and lower surfaces of each tube 23 by, for example, brazing.
The heat exchanger is manufactured, for example, in the following manner.
Welded pipes, formed as header pipes 22, are prepared. A plurality of connection holes 26, each having substantially the same shape as the peripheral shape of tubes 23, are formed on each welded pipe with a predetermined pitch in the axial direction of the welded pipe. Tubes 23 and radiation fins 24 are then arranged in order on the header pipes. Both end portions of the arranged tubes 23 are inserted into corresponding connection holes 26 of header pipes 22. Once the components are positioned, the portions to be connected are secured together by, for example, brazing.
The connection holes 26 in such a conventional heat exchanger are processed on the periphery of the welded pipe, formed as header pipe 22, after the welded pipe is made. This practice, due to the shape of the welded pipe, requires the use of a special jig or tool for processing the holes. This operation causes the manufacturing of the header pipe to be expensive. Consequently, difficulty is had in producing heat exchangers inexpensively. In addition, since it is generally difficult to form connection holes 26 precisely at predetermined positions on the periphery of welded pipe having a circular cross section, defects are liable to occur while inserting and connecting tubes 23 into the header pipes 22. Furthermore, the welded pipe is made merely by bending a flat plate in the form of a pipe and welding the side edges of the bent plate to each other. In this construction, the welded portion generally does not have a high strength, particularly against pressure. Therefore, cracks due to a high pressure fluid passing through the header pipes are liable to occur on the welded portion during use of the heat exchanger over a long period of time.
FIG. 19 shows another conventional heat exchanger 31 which comprises a pair of header pipes 22 with caps 27, a plurality of tubes 23, a plurality of radiation fins 24 and a pair of reinforcement members 25. In addition, heat exchanger 31 includes brackets 32, attached to the upper and lower portions of each header pipe, for supporting the heat exchanger. Each bracket 32 has a U-shaped slot 32a at its one end portion. The curved portion 32b of bracket 32 formed at other end portion is attached onto the periphery of header pipe 22 by, for example, torch brazing or tig welding.
In such a conventional heat exchanger, brackets 32 are attached to header pipes 22 after the header pipes 22 are made. As a result, many members for construction of the heat exchanger are necessary. Moreover, because the attachment of brackets 32 onto the peripheries of header pipes 22 is troublesome, it is difficult to produce the heat exchanger inexpensively. In addition, since brackets 32 are attached directly to header pipes 22, a corrosion (an electrocorrosion) is likely to occur at the attachment portion. If such a corrosion occurs, the rigidity of header pipes 22 decreases.